Archived - nice fusor pix, pinhole camera shots

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Doug Coulter
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Archived - nice fusor pix, pinhole camera shots

Post by Doug Coulter »

In preparation for our eventual "let us in the neutron club" post, I thought it would be nice to post a few of the supporting technologies we've used to get there first, so that post doesn't get cluttered with too many obscure details with the real run data buried in it (which was Richard's idea and I agree).

This was from a recent test run of a new grid, a new power supply and an improved pinhole charged particle/x-ray camera. This run wasn't particularly sucessful due to integrating the monster supply into the rest giving some troubles due to excess energy storage in it's CW stack, but a real run looks very little different in pictures, mostly dimmer when we are getting the highest reaction rate. By the time we run pressure up to the point of seeing the nice rays, we are current and heat limited. In a real run, you only see a dot in the middle of the grid, or looking down from the top, a line, about like a mechanical pencil lead in size.

The first two pictures show our pinhole camera, which is simplicity itself. This is a 2" long piece of 2" copper pipe, with a 1/8" thick piece of lead soldered on one end with a .05" hole in the middle, and a phosphor scrren we made inserted in the other end and held by he wires you can see. I got the pyex from McMaster for the screen, Eljen supplied the ZnS:Ag, and we used an old technique from CRT manufacture to stick the phosphor on there. The two pictures focus at different lengths, so you can see some detail on both the camera and what it's looking at. Sadly, the phosphor screen has so much dynamic range my (rather expensive) digital camera can't hack it, and it's overexposed. In person you can see more. Remember, an pinhole camera reverses the image, and it's easier to understand what you see here. The bright thing to the left of the grid is looking into the end of our uWave ion source, details of which will be another post, we like it a lot, it works great, and even shows up on the charged particle camera (to make it see only X rays, we put a Be window over the hole, but it is nowhere near as sensitive to them). I may try a Hemholtz coil arrangement on this as being more flexible -- shift charged particles in the image in a direction depending on which charge they have, leave the X rays unmoved, and learn more faster. Though this is mounted on a grounded wiggle stick, I'd bet we have some positive and neutral particles hitting hard enough to make light.

If anyone duplicates this, don't use plastic for the screen, it gets hot in there! Tried that and it lived less than one minute, ugly. In fact, I melted the solder joint holding it to the wiggle stick adapter in one run...next time, I braze that, but hey, the front is lead anyway....

We used a very dilute sodium silicate (about a drop in 25 ccs water) with a tiny amount of acetic acid added after letting the very tiny phosphor particles settle onto the screen evenly, then let it sit overnight, remove and dry. This is rev-2 model, where I sandblasted the side of the glass that got the phosphor, and we used less of it to make for sharper images, which sadly, don't photograph all that well.

In case someone wonders what they are looking at in the first two pictures, we are using a short-fat cylinder grid made of Ti wire and sheet here, about 1" OD by about 2" long. The red glow is alumina beads on the ion extraction electrode supply wire lighting up in X rays or charged particles, don't actually know which, but it's pretty. The random blue dots are some phosphor I spilled in there that is hard to get rid of. Other things, like some other deliberate screens and the quartz bakeout heaters also light up, it's quite a sight.

The third picture is an aerial view from a port on top of the tank so you can orient your internal picture better. This is running in a 6" ID by ~6" stub off a 14" diameter tank, so we can get view access to things easier (among other reasons). THis part of the run was done at relatively high pressure and low volts to make it easier to see -- when we are making neutrons in bunches, it's pretty dim in there.

You can see that even with a cylindrical grid, the rays come out of the center of it, just like with a sphere, and we've tried spheres here, but like the cylinders better -- less power loss and heating, and better access to certain kinds of observations.

The last picture is of some grids we've used. Note that with enough power you can melt almost anything, even light-for strength Ti like we did on the one at left, which was our most productive of neutrons with a lesser power supply that was 40kv at 12.5 ma. The bigger supply melted it, and surprisingly it still works fine! The big vane grid was designed for use as a "control grid" outside a smaller inner grid, also a vane grid. Trying to run the big one at high voltage doesn't work out that well, too much current, but if one is careful it will make some neutrons. The one on the left was used when the feedthrough let us put it all the way back in the stub, and the new one in the middle is the compromise for current setup issues, and seems the best of all so far.

Static pictures don't do this justice, most of the fun is with mark one eyeballs (that don't overload and see better resolution) and being able to move the pinhole camera around, because, after all, charged particles can be in curved trajectories and such, unlike photons, and at some positions we intercept more or less of them from particular places. It's a great learning tool indeed, and intended to supplement other in-tank instrumentation to come soon, as in accurate E field measurements, also on a wobble stick.

More later, have fun with this. If anyone needs help duplicating this, I'm here.
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Richard Hull
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Re: nice fusor pix, pinhole camera shots

Post by Richard Hull »

What you have displayed is a fusion image, this is for sure and for certain.

Interesting that the rays center in the cyinder's length! Un-expected. Wonder what this tells us?

Looking forward to the run reports, I am sure you will be doing significant fusion.

Richard Hull
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Doug Coulter
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Re: nice fusor pix, pinhole camera shots

Post by Doug Coulter »

Richard,

thanks, and yes, at times we are making a lot of bubbles and an He3 tube go nuts, but I'm waiting to post on that as we discussed -- I need to get some numbers *I* have more confidence in for one thing, and it seems wise to get this underlying stuff handled first anyway, so I can direct questions about them to these threads instead of mucking up that thread. For one thing, a recent acquisition of a cap manometer has allowed me to calibrate our other pressure gage for D, and that just happened last night, I have to get the cal equation made up for it. So, on that topic, now my gage agrees with yours...good, I didn't think the difference was anything to worry about other than gage calibration for the gas in use. It's the factory big buck one that's wrong on D in this range of pressures, btw.

I have only a guess right now why the rays come out of the middle and otherwise act as they do. If the grid sticks a little farther out, to the main tank, they still come out in the middle but are angled into the main tank instead of coming straight out radially. I'll know more when I put the pre-amped faraday probe pair in there instead of the camera on that wobble stick and will report, along with some tests with magnets and the right hand rule on the stick. At this point, other than intuition, one can't really even know which way the main particles in the rays are going -- in or out, though it sure looks like "out".

I will simply guess that at the center the negative field is least because near the ends there's more electrode close by, and that the rays are excited neutrals that came from....good question, whether they had just been ions and there was charge exchange from the grid or were neutrals excited and knocked out by ions, I just can't say from anything other than a gut feel, which I prefer not to put up here (much). Real measurements beat a guess any day, and I'll have those soon enough.

I will add that I am sure part of the pinhole camera image IS positively charged particles, as we can see just the ion source which only emits those, unless electrons are going backwards against a 4kv field in a 1/2" diamter 6" long tube, kind of unlikely, but again, putting a magnet on there will eliminate any doubts whatever.

I should add one construction detail. The 2" pyrex window there is slightly larger than the ID of 2" copper pipe, so we cut a little relief into that on the lathe to make it fit and sit flat behind the retaining wires. A minor job, but nice to have done.
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Dustinit
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Re: nice fusor pix, pinhole camera shots

Post by Dustinit »

Beautiful work Doug,
I also was surprised at the central focussing longitudinally.
Perhaps there are low energy electrons trapped in the cage that assist self focussing.
It would be interesting to see a cage where the grid wires curve inwards towards the centre in an hourglass shape to see if this spreads the beams along the length.
Excelent work and thanks for the eye candy.
Dustin
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Doug Coulter
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Re: nice fusor pix, pinhole camera shots

Post by Doug Coulter »

Thanks Dustin (and for your help in the past).

I too was surprised by that, and may have an explanation or few, but at this point it'd be arm-waving and wake the anti-trolls, so I desist for now. It's one of those things that seem obvious in hindsight, but not in foresight, and I will be taking measurements to see if my guesses are right soon. I get surprised enough by observation to realize my guesses are just that -- they might be informed scientific guesses, but still not a surety by any means.

This effect happens no matter which way the wires are bowed, or with perfectly straight vanes (all milled together in the same fixture). That I can say without getting into armchair conjecture, it's an observed fact. At HEAS I showed some pictures of this with a longer grid getting nearer the tank side of the stub, in in that case, they still emanated from the grid center, but then angled out into the large tank, so that's maybe a hint -- they were heading for the lower field gradient.

If there's a place where the wires are farther apart (normal construction imperfections etc) then the most ray comes out where the wires are the farthest apart. So if I mis-space one wire in an 8 wire grid, I may only get one ray out of the wider gap, no where else.

Getting that even pattern all around means this grid was more precise and it is -- I'm getting better at this.

What the pix fail to show, btw is that whem you move the pinhole camera, the image of course moves, but the brightness of this or that part may change radically. That's because from a different vantage point you may see more or less particles from a given source in there -- they may not be moving in straight lines like photons -- for sure, they are not. The difference can be as dramatic as looking at a laser beam from the side, vs being in the beam.
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Doug Coulter
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Re: nice fusor pix, pinhole camera shots

Post by Doug Coulter »

I am slightly disappointed that this got so little response. No, I'm not giving recipes to copy here that will get some copycat idiot into the 10 million neutron club tomorrow, but doing some real science and showing the way for others to do so as well. I'd hoped that there were more people interested in new things and ways to learn than I'm getting responses from, on this new charged particle/X-ray camera and what it may do for a serious researcher who wants to actually know what goes on in a fusor rather than sit in an armchair and pontificate without any real practical (or even theoretic) knowledge.

What gives with that? Is this the wrong time of year or something?

So flame me -- but better yet, what are *you* doing to advance this and not just copy others?
Show me up, I'd love it Let's get it on, guys!
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Mike Beauford
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Re: nice fusor pix, pinhole camera shots

Post by Mike Beauford »

Hi Doug,

You guys are way ahead of me with the design and implementation of your fusor. I am avidly watching what you and your crew are doing. If I'm quiet it's because I am still trying to figure out the physics regarding what the heck you are doing. Keep up the great work!

Mike Beauford
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Doug Coulter
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Re: nice fusor pix, pinhole camera shots

Post by Doug Coulter »

Well, you're not alone in that.

I have plenty of arm-waving potentially-BS theories, even pretty much having the underlying physics theory hammered - theory doesn't predict various types of emergent behavior that well, but does do so pretty well explaining it in hindsight. I choose not to post them just yet, as I would rather have it all locked up tight so the skeptics can't argue, at least not from solid ground, anyway.

Obviously, anything you can see visible isn't ions, it's something with electrons falling from one state to another at less than 3 ev energy difference. That's what makes this charged particle camera interesting, as it can see things my eyes cannot by themselves. Sadly, I can't put a movie up here, as the really cool stuff shows better as you move the thing around on the wobble stick, and though the image moves as you'd expect it to as the POV changes, different parts get bright and dim as they either are or are not actually in a "beam" of particles at a particular position. The charged particles, unlike photons, don't necessarily follow straight lines, and the picture from different angles reveals quite a lot about what're really going on. Beats armchair theorizing all day long.

This post was meant to prep for my neutron club post, to save clutter there. This is what it looks like at the higher currents, with all the nice rays. But I actually get more neutrons per second when the only thing you see (by eye) is the pencil focus at the middle, the rays barely visible at all to the eye.

Not quite the same thing I saw at HEAS this last time on Richard's record run, but that's what I see, saw, took pictures of, and believe.

Here's what I saw when I tried to dupe his grid.....It just got hotter than hades and no significant neutrons. The end seems to get hit quite a lot by ions, heating it up in my lashup, which isn't spherical.
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Re: Archived - nice fusor pix, pinhole camera shots

Post by Adam Szendrey »

Well now THIS is certainly very interesting to me! I was a bit surprised by the star mode of the cylindrical grid!
Might have to do with the length/diam. ratio of the grid in relation to that of the chamber.

Some further thoughts of mine on this phenomenon:
I think that unless the cylinder extends almost from top to bottom of the chamber (hard to actually do with a metal chamber), then a lot of ions will not be radially (using the cylindrical grid as our reference) accelerated, but instead at an angle, coming from "below" or "above" of the grid, hence their velocity vector will not be perpendicular to the grid wires, and they could end up focused more towards the center of the cage, creating a higher plasma density there. This would in theory create a more point-like focus instead of a linear one, and that's exactly what we see here. Although it should be a bit more smudged maybe, if this is the case. I have a feeling if we were to only accelerate ions from the chamber volume that is within the height of the inner grid (which would be like shrinking the chamber height to the height of the grid, the diameter would be the same of course), we'd see more of a string. Also the larger the chamber or outer grid is compared to the grid (regardless of shape), and the farther the majority of ions start from the grid, the more those ions would see the grid as a "point", and less as a linear target. Using a toroidal (from what I've seen when it was tried) grid we see a "ring" instead of a point focus. I think hat makes sense as the toroidal grid is simply not as "sensitive" to the size difference between it, and the chamber (or outer grid), given that it has a positive or ground "column" in the middle of course, otherwise (as it has been demonstrated) it'll give a point focus in the center of the torus. It would just be a looped cylindrical fusor basically.

"Tokagrid" by Mark Rowley here:
viewtopic.php?f=6&t=2457&hilit=tokagrid#p14662
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